Atrial Septal Defect

Liaison: Jan Young

An atrial septal defect is a hole between the upper two chambers of the heart.

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The heart of a dog (or person) consists of 4 chambers. The two upper chambers are called atria (singular atrium) and the two lower chambers are called ventricles. During embryonic development the heart begins as a simple tube, which later divides into the four chambers. The two upper chambers are separated into right and left by a septal wall or septum, as are the two lower chambers. During development, there may be failure of the septum to develop correctly, leaving a hole between the two chambers. In the case of the upper chambers, this hole is called an atrial septal defect (ASD). The defect can vary in size from very small to quite large. The size of the defect dictates the seriousness of the condition. The presence of a hole allows blood to flow directly from the left atrium into the right atrium because the pressure on the left side of the heart is much higher. Depending on the size of the hole, this can result in a significant increase in the work of the right side of the heart. If the defect is small, only a small amount of blood flows from the left to the right and there is not a significant increase in the work load of the right side of the heart.

Signs and Symptoms

If the ASD is small there may be no symptoms at all, although your vet may be able to hear a heart murmur. The murmur is caused by the turbulence of the blood flowing through the abnormal hole in the septal wall. Dogs with small ASDs typically live a normal life although they may have a tendency toward respiratory infections. With increasing size, signs and symptoms may begin. A heart murmur is again present but may have a different quality because of the larger size of the hole and sometimes because of turbulence of an increased amount of blood flowing from the right ventricle into the lungs. Dogs with larger ASDs may have exercise intolerance and/or have a bluish tinge to the tongue and/or mucous membranes. There may be retarded growth rate in young dogs. Because of the increased workload, the right side of the heart eventually fails and symptoms of congestive heart failure (CHF) appear. These may include the appearance of, or change in, an existing heart murmur, weight loss, difficulty breathing or shortness of breath, and mild to severe coughing. There may also be swelling or edema of the limbs and/or abdomen. These are the signs and symptoms of CHF, not of the ASD per se, and are the serious life-threatening concerns.

Causes

ASD is congenital (developmental defect) and is believed to be hereditary. It is relatively uncommon in dogs but Samoyeds have a higher frequency than most breeds.

Risk Factors

There are no known risk factors, although factors which interfere with prenatal development, such as toxins, might theoretically play a role.

Diagnostic Tests

Once your vet hears a murmur that does not disappear by 6 mos. of age, or there are any symptoms, diagnostic studies including an electrocardiogram (ECG), chest x-ray (CXR), echocardiogram, and perhaps an ultrasound (US) may be done. These studies will help determine the presence of an ASD and the degree, if any, of enlargement of the right side of the heart and thereby the severity of the disease progression.

Treatment Guidelines

Note: Treatment of animals should only be performed by a licensed veterinarian. Veterinarians should consult the current literature and current pharmacological formularies before initiating any treatment protocol.

There is no specific treatment for the ASD itself. Surgery options are expensive and have uncertain outcome. Treatment is aimed directly at the CHF and is initiated at the first signs. Treatment includes medications to support the heart and medications to decrease congestion in the lungs. Sodium restriction (to help prevent fluid retention) and exercise restriction are also usually prescribed.

Management

Because ASD is believed to be inherited, affected dogs or dogs with primary relatives with ASD should not be bred. Samoyeds used for breeding should have a cardiac examination by a veterinarian with advanced training in cardiology. If the results of the examination are normal and submitted to the Orthopedic Foundation for Animals (OFA), the OFA assigns an OFA number, certifying the dog as free from congenital heart defects.